I don't want to pay to heat the whole house? How can I completely shut off one zone?

I am living in a large house with radiators and two heating zones in New England. I have the thermostat set to the lowest possible setting in the zone of the house I don't use. Even at that, it is burning a lot of oil to maintain that minimum temperature. How can I shut off that zone and part of the house completely and avoid having the water in the pipes freeze? Would keeping the water circulating through the pipes and radiators be enough? There is no domestic plumbing in the part of the house I want to shut off.

The circulator running should keep pipes from freezing up. Something to think about; the walls that separate whatever side of the house you are going to be shutting down with the walls of the side you will be heating will now become cold walls. So, for arguments sake, they will be no different than an outside wall. Keep this in mind, are these walls insulated, or are you going to get a lot of heat loss from the warm part of the house to the cold part of the house. You may not recieve the savings you think you are going to get. If you feel like you are burning more oil than you should you may want to start thinking about, why? But, if you just simple dont want to pay for that much oil than I dont blame you.

The circulator running should keep pipes from freezing up. Something to think about; the walls that separate whatever side of the house you are going to be shutting down with the walls of the side you will be heating will now become cold walls. So, for arguments sake, they will be no different than an outside wall. Keep this in mind, are these walls insulated, or are you going to get a lot of heat loss from the warm part of the house to the cold part of the house. You may not recieve the savings you think you are going to get. If you feel like you are burning more oil than you should you may want to start thinking about, why? But, if you just simple dont want to pay for that much oil than I dont blame you.

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Even un-insulated there should still be significant savings as long as there is minimal air transfer between zones. The un-heated zone is still earth-coupled (assuming it's over a basement or sealed crawlspace), and will stagnate at temps well over the outdoor air temps if it's reasonably tight and has insulated exterior walls. Heat leaking in from common walls with heated zone will boost it too.

Standard 2x4 studwall partition walls with gypsum both sides, no cavity fill will deliver ~ R1.5 (similar performance to many brick exterior walls!) but unless they're air-tight you may run into condensation/mold deterioration issues in the closed off section, as the warmer air infiltrates into the colder part. Run a dehumidifier in there if you have to- keep the RH under 65% and it should be fine for the winter. Keep an eye out for mold/condensation on the heated side of the partition walls too. If the temp of the wall drops enough there'll be a boundary layer of saturated air, and mold can get started.

Is there a circulator for each zone? Depending on how the system is plumbed, you may not be able to run the circulator without supplying that zone heat. Without seeing it, it would be hard to tell.

Normally, the zone comes from the hot outlet of the boiler through the radiators, and back to the cold inlet of the boiler, pushed by the circulator. If there's only one, then the loop is controlled (opened) by a zone valve. Even if it has its own pump, unless special piping was installed and by-pass valves, there may not be a complete loop to run the water without running it through the boiler (and therefore heated).

Your question seems to be ambivalent. You do not want to heat that area with the thermostat, but you want water running through the system to keep it from freezing. What is the difference between it running periodically from the thermostat, and running ALL the time without it? Other than that constant operation should use much MORE energy than intermittant operation. Unless I am missing something here, you have not thought out the consequences of your proposal. And heat ALWAYS tries to move to cooler areas, regardless of what the walls are made of. Insulation slows it down, but does not stop it, and your internal walls being uninsulated will hardly even slow it down as it tries to warm up the vacant areas.

Won't the water circulating still be heating the area ?
My boiler does not have any setup to bypass the boiler simply to circulate water

My 2nd floor is unheated at present & only dips to about 36f w/R30/38 insulation in cold weather
Usually it stays around 45-50
The 1st floor ceiling was insulated at some point with R25, accessed from the 2nd floor

Several companies make units that will turn the circulator on for a brief period of time to prevent freezing also.

And yes, if it went down to 9 he may very well have frozen pipes.

When it gets really cold out folks try to save money by turning things down or off, often leading to frozen pipes and damage that ends up costing way way more than running the heat would have. Best advice. Keep the thermostats where you normally set them and wait the cold out.

I reconnected the thermostat early this morning. Is it possible to leave the thermostat wired to the circulator but disconnected from the boiler? I'm thinking this way the circulator would circulate but the boiler would not fire. Or does the boiler kick on when the store of water in it drops below a certain temperature and not when instructed by the remote thermostat? The system is not plumbed to bypass the boiler.

Some boilers can run from cold...some maintain some minimum temperature, regardless of the call for heat. When there has been no call for heat for awhile, what temp is the boiler water? This is normally controlled by an aquastat. It sets the min/max of the boiler.

The remote thermostat for the zone I want to shut down is a mercury triggered type with a minimum setting of 50 degrees. I thought of skewing the horizontal alignment of the mounting to over ride the settings. Anyone ever done this?

I am not familiar with the aquastat. Is it adjustable? The boiler is a Weil McClain Gold and about three years old. Can I disconnect the thermostat from the boiler and leave it connected to the circulator?